1. Field of the Invention
The present invention relates to a twin extruder, and more specifically to a twin extruder where an underwater cutting apparatus is connected, via a gear pump, to a side portion or a lower portion of a cylinder which houses therein twin screws whose both ends are supported.
2. Related Art
This kind of twin extruder conventionally used is composed as shown in FIG. 3. In the same, reference numeral 21 designates a cylinder in which a pair of first screw 22 and second screw 23 are disposed. Both screws 22, 23 are sealed at both ends thereof with sealing members 24, 24a, and supported by not shown bearings.
Both screws 22, 23 are composed of a material supplying section 25 having a flight of small lead and a kneading section 26 having a flight of large lead. The flights of both screws 22, 23 are inverse helical screws with respect to each other. Both screws are rotation driven by a not shown motor outward or inward each other (in this case, the flight is the inverse helical lead with respect to the figure), when seeing the upper parts of the screws from a drive source.
The cylinder 21 is provided with a material supplying hopper 27 about the upper part thereof corresponding to the material supplying section 25.
The cylinder 21 is provided with an discharge port 28 at the side or lower part thereof positioned at the downstream of the kneading section 26. The discharge port 28 is provided in order with a gear pump 29, a screen changer 30, a die 31 and an underwater cutting apparatus 32.
Explanation will be made to actuation of the above mentioned twin extruder.
Resin material charged into the cylinder 21 from the hoppers 27 is transferred to the material conveying section 25 and the kneading section 26, and is molten and kneaded. The molten and kneaded resin is sent to a downstream gear pump 29 from the discharge port 28, goes through the screen changer 30, the die 31 an the underwater cutting apparatus 32, and pelletized.
Since the prior art twin extruder is composed as mentioned above, there exist the following problems.
(a) Since the axes are sealed under pressure with sealing members at the side of the discharge port of the cylinder, secure sealing is difficult.
(b) Since thermal expansion should be absorbed at the discharge port, centering of the underwater cutting apparatus is difficult.
(c) With respect to the diameter of the screw, amounts to be processed are limited.